CPU Overclocking vs. Power Consumption. Page 11

Processor power consumption is closely connected with their clock frequency. That is why when overclockers increase their system performance they sacrifice energy efficiency. But how serious this problem actually is? We tested nice different processors from Athlon II, Core 2, Core i3, Core i7 and Phenom II families overclocked to different levels and are ready to give you an extensive answer to this question.

Intel Core i7-950

There is one more platforms that Intel positions for the upper price range – LGA1366. CPUs designed for this platform are built around the same Nehalem microarchitecture, but they still have a few peculiarities of their own. It is these particular peculiarities that determined our decision to include these processors into our today’s test session devoted to system power consumption during overclocking. We chose a relatively inexpensive solution - Core i7-950. This CPU is based on 45 nm Bloomfield core that should be considered the first Nehalem silicon incarnation. Just like other LGA1366 processors (except the latest Core i7-980X), Core i7-950 has four computational cores, built-in triple-channel memory controller and a QPI bus controller (this bus connects the CPU with the chipset). I have to say that unlike LGA1156 systems, the PCI Express graphics bus controller in LGA1366 systems is located in a more traditional spot – the chipset North Bridge rather than CPU.

Speaking of the specific CPU we chose, Core i7-950, we have to say that its nominal clock speed is set at 3.07 GHz, but due to Turbo Boost technology it can overclock to 3.33 GHz under partial load. It also supports Hyper-Threading technology. Each of the four cores has its own 256 KB L2 cache. There is also an 8 MB shared L3 cache.

One thing immediately catches our eye: the core voltage of our test Core i7-950 is set at 1.2 V, which is higher than the core voltage of the Core i7-860 with the same microarchitecture. The voltage of the North Bridge integrated into the processor was also higher: 1.2 V instead of 1.1 V. And there is a reason for these differences. The TDP set for Intel LGA1366 processors is 130 W instead of 95 W, which means that the manufacturer takes into consideration higher voltages. Of course, it affects the power consumption of LGA1366 systems. In nominal mode we registered 190 W power consumption in our system equipped with Core i7-950 processor, which gives us every reason to regard LGA1366 platform as one of the most power-consuming configurations.

Despite this high power consumption and heat dissipation, Core i7-950 handles overclocking pretty well. We managed to get this processor to run stably at 4.2 GHz frequency. Up until 3.6 GHz this CPU overclocked even without any voltage increase. To build graphs showing the dependence of power consumption and currents on the frequency, we once again took some measurements with a 200 MHz increment. The table below shows all corresponding settings:

Note that the clock frequency multiplier of our Core i7-950 is locked that is why we overclocked this processor by raising the base clock frequency. However, due to Turbo Boost technology, we can set the multiplier one point higher than its nominal value.

The graph showing dependence of system power consumption on the CPU clock frequency under maximum load is of pretty typical shape:

I have to say that LGA1366 platform consumes a lot of power not only in its nominal mode. Things get even worse during overclocking, which is in fact, not surprising at all, because we have to increase the processor Vcore in order to ensure stability at high clock frequencies. As a result, at 4.2 GHz our Core i7-950 consumes 127 W more power than in nominal mode. Note that during our overclocking tests we only changed the CPU settings, that is why we owe almost the entire power consumption increase to the processor.

To prove it we would also like to show you the graph for mainboard currents:

The current going along the 12 V processor line more than doubles during overclocking. At the same time you should remember that the CPU takes some power that goes to the integrated North Bridge from the mainboard. Therefore, the increase in power consumption along the 5 V line should probably also be assigned to the CPU. And by the way, even though the power consumption of the Core i7-950 working at 4.2 GHz frequency looks quite dramatic, the currents in the power lines do not really increase too much up until 3.8 GHz frequency. That is why even in LGA1366 systems the biggest power consumption increase occurs only when we start raising the voltages.